7 alpha-methyl-19-nortestosterone facilitates sexual behavior in the male Syrian hamster

Steroid hormones from the testes promote attraction to estrous females and facilitate copulation in the male Syrian hamster. We compared the ability of testosterone (T) and MENT, a potent synthetic androgen that does not undergo 5 alpha-reduction, to maintain sexual behavior in castrated males. Steroid treatment was initiated immediately after castration at three levels by means of Alzet osmotic pumps in sexually experienced adult male hamsters. Daily doses were 5, 25, or 100 micrograms T and 1, 5, or 25 micrograms MENT (n = 5/group). Additional castrated males (n = 5) remained untreated. Sexual behavior was recorded during two 10-min tests before, and at 2, 4, 6, and 8 weeks after orchidectomy. MENT and T maintained equivalent levels of behavior at each corresponding dose of androgen (high, medium, or low). The low dose of T or MENT failed to sustain mating behavior. Eight weeks after castration, males receiving the high and medium doses of androgens continued to express intromissions and ejaculations at gonadally intact levels. However, only males receiving the high dose showed anogenital investigation at the same level as intact males. From these data, we conclude that MENT sustains mating behavior in the male hamster, and that chemoinvestigatory behavior requires higher levels of androgens than those necessary for copulation.